As a plant that includes a steam turbine, there is a combined cycle plant that includes a gas turbine and an exhaust heat recovery boiler that generates steam using an exhaust gas from the gas turbine and sends the steam to a steam turbine.
The combined cycle plants include single-shaft combined cycle plants in which a gas turbine rotor and a steam turbine rotor are mechanically connected to each other, and multi-shaft combined cycle plants in which a gas turbine rotor and a steam turbine rotor are not mechanically connected to each other.
The starting time of the steam turbine changes according to a temperature of the steam turbine at the start of operation of the steam turbine. The operation starting time is described in detail in the following Patent Document 1. In Patent Document 1, for example, in a cold state where a metal temperature of a first-stage blade in a steam turbine is close to room temperature, the operation starting time is about 260 minutes. Further, in a hot state where the metal temperature is close to a temperature in a steady operation state, the operation starting time is about 35 to 70 minutes. Further, in a warm state where the metal temperature is a temperature between the cold state and the hot state, the operation starting time is 100 minutes.
That is, in the steam turbine, as an internal temperature of the steam turbine at the start of the operation becomes lower, the operation starting time becomes longer.